It has been proposed to form such a core with respect to the outer members, in a manner such that there will occur in one of the vibratory directions a reduction in the spacing between it and the outer members to increase the spring rate of the mounting assembly, with the core member comprising flyweights whose spacings from the core member are adjustable.
In such a mounting arrangement, the core member is caused to rotate when an axial force is acting on the engine mount, because it is urged in each section by beveled and angled surfaces to move outwardly towards the opposite side. The flyweights can be threaded, to a greater or lesser extent, out of the radial bores provided in the core member, which will enable the moment of inertia of the core, and thus the inherent frequency of the system, to be varied. This generates upon the occurrence of a force which is induced by an irregularity in the road surface and which is acting on the chassis, a counterforce which will inhibit covibration of the engine and thereby prevent reverse coupling to the body. This allows the acoustic tuning and the tuning of the vibratory comfort to be carried out separately.
However, due to the fact that the flyweights are arranged on the outside of the core member, such a mounting assembly is relatively bulky. Furthermore, the moment of inertia can be varied only within a very narrow range.